Perry Bacon Jr., of FiveThirtyEight, analyzes this development from all sides, including pros and cons for Trump himself, Republicans, Democrats, and the American people:
Trump can now say there is an independent investigation going on, by someone he did not personally appoint and who is not beholden to his party. [But] Mueller’s appointment ensures that the Russia controversy won’t just go away — at least not anytime soon. And he could gravely threaten Trump’s presidency if he finds clear, improper connections between the president’s campaign and Russian officials.
Republican members were being repeatedly asked about the Trump investigation. Like Trump, they can now defer to Mueller’s probe. The one problem? Mueller is only investigating the Russia issue. It’s likely Trump will do something else controversial — in the past two weeks alone, he allegedly shared highly classified intelligence with the Russians, and he fired Comey in a clumsy way that created all kinds of political problems. Republicans will still have to answer for Trump’s other controversial moves.
Democrats strongly disagree with Republicans like Mitch McConnell and Paul Ryan on policy, including on sweeping issues currently on the congressional docket such as health care and taxes. In the eyes of many Democrats, Trump and the potential laws he might sign could damage the country for years to come. A process that could (in the long run) lead to Trump’s removal from office is a major step for liberals.
In the short term, they may have lost an issue. Democrats could have pounded Trump and Republicans on their lack of accountability every day till next year’s midterms. Make no mistake: If Democrats had won control of Congress next year and Trump had blocked a special counsel up until then, impeachment would have been on the table. Now, Democrats have to wait and see what Mueller concludes.